This invention relates to a wheel speed sensor unit and a wheel bearing assembly carrying the wheel speed sensor unit.
Wheel speed sensors are mounted on wheel bearings to supply wheel speed signals, for example, to an ECU of an ABS.
A typical such wheel speed sensor unit includes an encoder mounted on a rotary member of the vehicle, and a sensor mounted on a stationary member so as to oppose the encoder. Japanese patent publication 8-281018 discloses an arrangement in which a flange-like rotary disk is provided on the rotary member outside a seal for sealing the gap between the fixed member and the rotary member, and a multipolar-magnetized encoder is mounted on the outer end face of the disk. The encoder is exposed to the outside.
Japanese utility model publication 7-36288 discloses an arrangement in which an encoder is provided between two rows of raceways on an inner ring of a wheel bearing assembly, and a sensor is inserted in a hole formed in the outer ring so as to oppose the encoder. The encoder is thus mounted in a sealed space.
In the arrangement shown in Japanese patent publication 8-43411, an encoder is arranged on an outer surface of a rotary member on a side inboard of the bearing, a seal member is mounted on the inboard side of the fixed member, and a sensor is mounted inside the seal member so as to oppose the encoder. The encoder is mounted inside the seal member and outside the bearing.
The first arrangement has a drawback that magnetic powder tends to adhere to the surface of the magnetized encoder during use. This may cause deterioration in the pitch accuracy. The second arrangement has a drawback that the axial dimension for mounting the encoder and sensor is not sufficient. In the third arrangement, since the encorder and the sensor have to be arranged inside of the seal member, the axial dimension of the inboard side end of the stationary member has to be accordingly large.
An object of the invention is to provide a rotating speed sensor unit which includes a seal for preventing entry of foreign matter and which takes up smaller mounting space and thus can be mounted on a wheel bearing assembly without increasing the axial dimension of the stationary member, and to provide a wheel bearing assembly having such a sensor unit.
With the rotating speed detecting device, the encoder rotates integrally with the rotary member and the sensor detecting portion detects its rotating speed. Since this arrangement is an inside-mount type in which the encoder and the sensor are protected by the sensor seal member, entry of dust and debris such as magnetic powder and other foreign matter is prevented. Also, since the seal member is mounted on a portion of the sensor, it is not necessary to provide a mounting portion for the seal member on any other part. Also, the encoder can be mounted in the gap between these parts.
Also, by mounting the seal member on the rotary member inboard of the sensor, bringing the seal lips of the seal member into sliding contact with a seal land formed on the inner surface of the fixed member, and arranging the encoder so as to oppose the sensor detecting portion inside of the seal member, it is possible to detect the rotating speed while preventing entry of foreign matter.
According to this invention, there is provided a wheel bearing assembly comprising a fixed member adapted to be fixed to a vehicle body, a rotary member rotatably supported in the stationary member through a bearing and adapted to be mounted to a vehicle wheel, an annular sensor fitted in the fixed member on an inboard side of the bearing and having a sensor element, a sensor seal for sealing a gap between the fixed member and the rotary member, the sensor seal being fitted in the annular sensor on an inboard side of the sensor element and having a seal lip kept in slide contact with a seal land formed on the rotary member, and an encoder mounted on the rotary member in a space between the sensor seal and the bearing so as to oppose the sensor element of the sensor.
With this wheel bearing assembly, the load of the vehicle body is supported by the wheels through the bearing, and the rotating speed of the rotary member which rotates with the wheels is detected by the rotating encoder and the sensor opposing it. Since this arrangement is an inside-mount type in which the encoder and the sensor are provided inside the seal member, foreign matter entering from outside is prevented by the seal member. Also, since the seal member is fitted in the inner surface of the sensor at one end, it is not necessary to provide a mounting portion for the seal member on the fixed member. Thus, the encoder can be housed within the width of the sensor, so that the encoder and the sensor can be mounted with enough room of space.
In another embodiment, a sensor is fitted in the fixed member on an inboard side of the bearing, a sensor seal for sealing a gap between the fixed member and the rotary member is fitted on the rotary member on an inboard side of the sensor element and has a seal lip kept in slide contact with a seal land formed on the fixed member, and an encoder is mounted on the rotary member in a space between the sensor seal and the bearing so as to oppose the sensor element of the sensor.